b 1. Field of the Invention
This invention relates to new and useful improvements in drilling jars and more particularly to double acting hydraulic drilling jars and the like.
2. Brief Description of the Prior Art
A fishing job, in oilfield terminology, means removing something from the well bore that does not belong there. What is removed is called a "fish" and may be part of a drilling string which has become stuck when drilling an oil or gas well, or may be production equipment being removed from an existing well bore during a workover or repair operation. The accepted method of retreiving a fish is to grab it by some means and push or pull an axial strain on it until something gives. A jar is a tool employed when either drilling or production equipment has become stuck to such a degree that a straight push or pull from the surface is insufficient to dislodge it.
The jar is normally placed in the pipe string in the region of the stuck object and allows the drilling rig operator at the surface to deliver an impact blow at the fish through manipulation of the drill pipe string. Jars contain a spline joint which allows relative axial movement between an inner mandrel or housing and an outer housing without allowing relative rotational movement. The mandrel or inner housing contains an impact surface or hammer, which contacts a similar impact surface or anvil on the housing when the jar has reached the limit of axial travel. If these impact surfaces are brought together at high velocity, they transmit a very substantial impact to the fish due to the mass of the pipe above the jar.
Prior art jars are of three distinct forms, viz. hydraulic jars, mechanical jars and bumper jars. The bumper jar is used primarily to provide a downwardly directed impact blow. The bumper jar is usually a splined joint with sufficient axial travel allowed so that the pipe can be lifted and dropped, causing the impact surfaces inside the jar to come together to deliver a downward impact blow to the fish. Mechanical and hydraulic jars differ from the bumper jar in that they contain a tripping mechanism which retards the motion of the impact surfaces relative to each other until an axial strain, either tension or compression, has been applied to the pipe. To jar upward, the pipe is stretched by an axial tensile pull applied at the surface. This tensile force is resisted by the tripping mechanism of the jar long enough to allow the pipe to stretch and store potential energy. When the jar "trips", this stored energy is converted to kinetic energy causing the impact surfaces of the jar to move together at a high velocity. To jar downward, the pipe weight is "slacked off" at the surface to put the pipe in compression. This compressive force is resisted by the tripping mechanism of the jar to allow the pipe to compress and store potential energy. When the jar "trips", the potential energy of pipe compression and pipe weight is converted to kinetic energy causing the impact surfaces of the jar to come together at a high velocity. Hydraulic and mechanical jars are much more efficient than bumper jars because they allow a much greater impact at the fish for a given pipe strain.
Most fishing jobs require that both an upward and downward jar be available in the fishing string. For example, during the drilling of an oil or gas well, the pipe may become stuck due to hole sloughing or differential pressure sticking such that it would be desirable to jar the pipe upward. Or the pipe might become lodged in a keyseat while "tripping" (removing the pipe from the well bore--do not confuse with tripping the jar) in which case it would be desirable to jar downward on the stuck point. Another example occurs when fishing for production equipment such as packers or pumps. Normally the tubing or rod above the stuck point is cut off and the fishing string is attached to the tubing or rod left in the bore by means of an overshot. A series of upward blows is initiated to attempt to dislodge the fish. If the fish can not be dislodged readily from the well bore, it becomes necessary to deliver a downward impact to the overshot in order to release it from the tubing or rod.
Various combinations of jars are used to achieve this two direction jarring action. A mechanical or hydraulic jar may be double acting such that it jars both up and down. Or an up jarring tool may be run with a separate down jarring tool. Whether combined into the same tool or embodied into separate tools, the jar must operate in either direction independently of the other to be fully effective and efficient. That is, the tool should trip in one direction, recock and trip in the same direction again without inadvertently, or of necessity, tripping in the opposite direction. Also, the recocking of the tripping mechanism in one direction should not be retarded by the tripping mechanism in the opposite direction.
Mechanical jars are generally less versatile and reliable than hydraulic jars. One design of mechanical tripping mechanism requires that the tripping load be selected and preset at the surface to trip at one specific load. If it is desired to increase or decrease the tripping load, it is necessary to pull the pipe from the well bore, a costly and time consuming procedure. Another mechanical tripping mechanism of known configuration requires that torque be applied from the surface through the pipe to the tripping mechanism and that this torque be maintained while the jar trips. This can be dangerous to personnel on the rig floor and makes the tripping load difficult to control in deviated well bores. Another weakness of mechanical tripping devices is that they must be run in the cocked or detent position. Thus, the tripping mechanism is subjected to stresses during the normal course of drilling if it is run as a part of the bottom hole assembly. Mechanical tripping mechanisms have the additional disadvantage that the metallic parts must move relative to each other while under a high compressive load. This causes rapid wear and frequent failure of the moving parts.
Hydraulic tripping mechanisms are more desirable because they afford the versatility of a variable hitting load controlled only by the amount of axial strain applied at the surface. Also, hydraulic tripping mechanisms are less subject to mechanical deformation and wear than mechanical tripping mechanisms and therefore will work for a longer time under the same conditions. However, present hydraulic tripping mechanisms operate in one direction only and require two tripping mechanisms to be run in tandem in order to achieve a double acting jar function. This requires two separate hydraulic fluid chambers, two valve systems, two metering systems, and sufficient axial travel to operate either mechanism independently. The result is a long and expensive tool with long splines and seal surfaces.
The patent literature disclosing drilling jars has developed largely within the last thirty years.
Storm U.S. Pat. No. Re. 23,354 discloses a very early form of double acting hydraulic jar. This jar utilizes the dashpot principle with a piston section moving through a cylinder of reduced diameter so that flow of hydraulic fluid is restrained from flowing from one side of the piston to the other. This drilling jar has the disadvantage that it must be fully operated in one direction in order to reset it to operate in the opposite direction.
Chenoweth U.S. Pat. No. 3,349,858 discloses a single acting (upward) hydraulic drilling jar in which the oil flow through the piston is controlled by a constant flow regulator valve.
Berryman U.S. Pat. No. 3,735,827 discloses a hydraulic fishing jar requiring a compressible hydraulic fluid. The mandrel is moved until the hydraulic fluid is compressed to a selected degree at which point a control valve engeges an adjustable tripping abutment which opens the valve and dumps the pressurized fluid through a bypass to permit rapid movement of the hammer relative to the anvil surface.
Berryman U.S. Pat. No. 3,797,591 discloses a hydraulic fishing jar similar to U.S. Pat. No. 3,735,827 but including a different adjustable trigger mechanism.
Berryman U.S. Pat. No. 3,851,717 discloses a hydraulic fishing jar having a constant flow bypass for a tripping piston and arranged so that the tripping piston is moved down until the main bypass valve is opened and the device trips.
Berryman U.S. Pat. No. 4,059,167 discloses a fishing jar similar to Berryman '717 and incorporating a tandem piston arrangement to lower the internal operating pressure.
Young U.S. Pat. No. 3,285,353 discloses a fishing jar having telescoping mandrels, one connected to the drill string and the other to the drill fish, surrounded by an outer housing. A piston valve is arranged to dump pressure after a selected degree of movement and to move the housing to impact a hammer surface against an anvil surface.
Hazen U.S. Pat. No. 3,087,559 discloses a hydraulic fishing jar having mechanical trip fingers with a hydraulic delay.